Drafting table construction

ABSTRACT

A drafting table including a pedestal, support columns mounted on said pedestal for generally vertical movement, and a drafting board mounted for tilting movement on the upper end of said support columns. The tiltable mounting for the drafting board includes pivotally connected first and second parts, the first part being secured to the board and the second part being secured to the support columns by a fastener and wedge arrangement. A counterbalancing mechanism is provided between the pedestal and the support columns to assist in raising and lowering the columns and the board. The mechanism includes means for adjusting the amount of counterbalancing force by braking or anchoring one end of a spring and raising or lowering the column assembly.

O United States Patent [151 3,638,584

Cisler et al. Feb. 1, 1972 [54] DRAFTING TABLE CONSTRUCTION 3,370,556 2/1968 Kool ..l08/l36 [72] Inventors: gar]! 315:2; \zllilslllam A. Gelbuda, both Primary Examiner fiancis K. zugel Assistant Examiner-Glenn O. Finch [731 Assignee: American Hospital Supply Corporation, Attorney-Hibben. Noyes & Bicknell Evanston, Ill. 22 Filed: May 21,1969 [57] ABSTRACT [21] APPL NOJ 826,478 A drafting table including a pedestal, support columns mounted on said pedestal for generally vertical movement, and a drafting board mounted for tilting movement on the U-S- ..108/6, upper end of aid upport columns The mounting for 5/ 12 the drafting board includes pivotally connected first and [58] Field Of Search ..l08/ll0, l36-144, Second parts, the first part being secured to the board and the 108,50 second part being secured to the support columns by a fastener and wedge arrangement. A counterbalancing [56] Ree'mces and mechanism is provided between the pedestal and the support UNITED STATES PATENTS columns to assist in raising and lowering the columns and the board. The mechanism includes means for ad usting the May et ai. amount of counterbalancing force or anchoring 3,140,559 7/1964 Grow alt "log/6 one end of a spring and raising or lowering the column as- 3,l83,860 5/1965 Kritske 108/2 Semb|y 3,213,809 [0/1965 Kritske ..108/2 3,273,517 9/1966 Amthor, Jr. et a1 108/2 8 Claims, 7 Drawing Figures PATENTEDFEB 1m 3.538.584

SHEEIE M Q PATENTED EB 1 W2 SHEET 3 OF Q DRAFTING TABLE CONSTRUCTION A drafting table of the character disclosed in Grow et al. US. Pat. No. 3,140,559 and in Amthor et al. US. Pat. No. 3,273,517 includes a pedestal or base unit, a support column assembly movably mounted on the pedestal, and a drafting board tiltably mounted on the column assembly, the foregoing components enabling adjustment of the height and the angle of tilt of the drafting board. A height-counterbalancing mechanism is connected between the pedestal and the column assembly to assist the draftsman in moving the assembly, and a tilt-counterbalancing mechanism is connected between the column assembly and the board to assist the draftsman in tilting the board. Both counterbalancing mechanisms are made adjustable so that different weights on the board may be accommodated, and brakes are provided to hold the column assembly and the board at a selected height and a selected angle or tilt.

In each of the drafting tables shown in these patents, the brake for holding the board at a selected angle comprises a first group of friction plates fastened to the column assembly and a second group of plates fastened to the board, the plates of the two groups being interleaved, and means for pressing the plates together to effect engagement of the brake. While such a brake works well, the brake shown in the Grow et a]. patent is relatively expensive and difficult to assemble because a large number of parts are required, and means is required to hold portions of the plates in each group in spaced relation. The corresponding brake shown in the Amthor et al. patent is also relatively expensive and difficult to assemble for the same reasons, and pivot members, in addition to the brake are required to support the board.

The height-counterbalancing mechanism in the Amthor et al. patent includes a torsion spring, and a worm and gear arrangement for adjusting the amount of the counterbalancing force. Such a torsion spring works well but the worm and gear are difficult to turn when an adjustment is necessary.

In accordance with the present invention, the foregoing disadvantages are avoided in a drafting table comprising a pedestal, a counterbalanced column assembly movably mounted on the pedestal, and a drafting board tiltably mounted on the column assembly, novel mounting means for tiltably mounting the board on the upper end of the column assembly. The novel mounting means comprises pivot means wedged in an opening formed in the upper end portion of the column assembly, a fastener means holding said pivot means wedged in said opening, and means for pivotally connecting said pivot means to said board, and novel adjustable counterbalance mechanism for assisting in moving the column assembly. The novel adjustable counterbalance mechanism comprises a torsion spring having one end connected to a drive mechanism for the column assembly, clutch means for connecting the other end of the spring to said drive mechanism, and brake means for connecting the other end of the spring to said pedestal. The clutch means and brake means are separately engageable to the drive mechanism and pedestal respectively. The counterbalance force is provided by the torsion spring which tends to unwind and move the board and column assembly upwards thus overcoming the weight of the board and column assembly. The counterbalance force is proportional to the displacement or number of turns in the spring. By using the clutch and brake means provided in the novel counterbalance adjustment mechanism and by raising or lowering the board, a draftsman can vary the number of turns in the spring and thus adjust the counterbalance force as is described in more detail hereinafter.

Objects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures of the drawings, wherein:

FIG. 1 is a front elevational view of a drafting table embodying the invention;

FIG. 2 is a side elevational view of the right-hand side of the drafting table as shown in FIG. 1;

FIG. 3 is an enlarged sectional view taken on the line 33 of FIG. 1;

FIG. 4 is an enlarged fragmentary view taken on line 4-4 of FIG. 1;

FIG. 5 is an enlarged fragmentary sectional view taken on line 5-5 of FIG. 3;

FIG. 6 is an enlarged fragmentary sectional view taken on line 66 of FIG. 3; and

FIG. 7 is an enlarged fragmentary sectional view taken on line 7-7 ofFlG. 3.

In greater detail, a drafting table embodying the invention comprises a base unit 21 (FIGS. 1 and 2), a support column assembly 22 mounted for generally vertical movement on the base unit 21, and a drafting board 23. The latter is tiltably connected to the support column assembly 22.

The base unit 21 is a generally rectangular unit and is adapted to be supported on the floor by a pair of outriggers 24 each having a pair of legs. The base unit 21 comprises two pedestals 26 joined by a lower panel 27, a back panel 28, an upper panel 29 and a top 31. The base unit 21 houses and supports the column assembly 22 with portions of the latter extending above the base unit. The base unit 21 also houses a drive mechanism 32 for moving the column assembly vertically and a height-counterbalance mechanism 33 for the linear movement of the column assembly 22. The top of the base unit 21 has openings 34 (FIG. 3) through which the column assembly 22 extends.

The support column assembly 22 comprises a pair of laterally spaced columns 36 (FIGS. 1 to 3) and a horizontally extending connecting member in this instance in the form of a channel 37 (FIGS. 1 and 5) which extends between and is rigidly secured to the upper ends of the columns 36. Each column 36 is movable on and supported by a support in the form of a channel 38 (FIGS. 3 and 6) which extends upwardly from the bottom of the base unit 21, and the lower end of each channel 38 is fastened to base unit 21. Each column 36 is movable relative to its associated channel 38, and is guided for such movement at its lower end by a pair of lower rollers 39 (FIG. 3) secured to the column 36 and bearing against a channel 41 (FIG. 6) secured to the base unit 21. At its upper end each column 36 is guided by an upper roller 42 (FIG. 3) secured to the base unit 21 adjacent the opening 34 and riding on the outer surface of its associated column 36. As shown in FIG. 3, the column assembly 22 is canted upwardly and forwardly toward the draftsman, with the upper rollers 42 bearing against the forward sides of the columns and the lower rollets bearing against the forward sides of the channel 41.

Each column 38 of the column assembly 22 is provided with a brake mechanism 43 (FIG. 3) to retain the column assembly in an adjusted position. Each brake mechanism comprises a brake rod 44 (FIGS. 3 and 6), a retainer in this instance in the form of a wire coil 46, a brake link 47, a pivoted brake pedal 48, a pivoted brake arm 49, and an actuating spring 51. The ends of each brake rod 44 are secured to the associated column 36. The coil 46 encircles the rod 44, the ends of the coil being secured to the brake arm 49 as by screws. The brake arm 49 is pivotally secured to the upper end of the associated channel 38, and is connected to the rear end of the pedal 48 by the brake link 47. The lower end of link 47 is pivotally fastened to the rear of pedal 48 and the upper end of the link is hooked over a portion of arm 49 and is slideable in that portion of the arm. Downward movement of the front end of the pedal 48 results in upward movement of the link 47. Brake-actuating spring 51 is connected between the base unit 21 and the front end of the pedal 48 and urges the rear end of the pedal 48 downwardly so that the brake arm 49 is caused to pivot and cant the coil 46 relative to the brake rod 44 and thereby cause the coil 46 to frictionally engage the rod. Application of sufficient foot pressure on the pedal 48 overcomes the force of the actuating spring 51 and slides the upper hooked portion of the link 47 out of engagement with the arm 49. The brake arm 49 is then free to pivot and the coil 46 is loose on the rod 44 permitting free adjustment of the columns 36.

The drive mechanism 32 (FIGS. 3 and 6) ensures that the two support columns 36 move in unison, and comprises a laterally extending timing shaft 56 which is rotatably mounted on the base unit 21, a rack 57 secured to each column 36, and two spur gears 58 on the shaft 56 and engaging the racks 57. The timing shaft 56 is rotatably mounted in the base unit 21 as by bearings 61, and the two spur gears 58 are secured to opposite ends of the timing shaft 56 as by keys (not shown). The spur gears 58 engage the racks 57, and rotation of the timing shaft 56 causes linear motion in equal amounts of the two columns 36.

The drafting table may or may not be provided with a power drive for moving the column assembly 22. In the present instance, a power mechanism 62 is provided, comprising a motor 63 (FIG. 2), a toothed drive pulley 64, a toothed driven pulley 67, a timing belt 68, and a motor control switch (not shown). The switch is connected to be actuated by movement of the foot pedal 48, whereby downward movement of the pedal 48 results both in release of the two brake mechanisms 43 and also energization of the motor 63. The motor 63 is wired so that a first movement of the pedal 48 causes the motor 63 to rotate in one direction, and a second movement of the pedal causes the motor to rotate in the opposite direction. Drive pulley 64 is secured to the drive shaft of the motor 63, and the driven pulley 67 is secured to one end of the timing shaft 56. Thus, energization of the motor 63 will cause rotation of the timing shaft 56 and movement of the column assembly 22.

The height-counterbalance mechanism 33 is provided to facilitate movement of the column assembly 22, and includes a torsion spring 71, the counterbalance mechanism being adjustable. One end of the torsion spring 71 is connected to the drive mechanism 32 and the other end is connected to the base unit 21. For adjustment the counterbalance mechanism 33 comprises an intermediate element (intermediate in the sense it is a connection between the column assembly and the base unit), in the form of a gear 73 (FIGS. 6 and 7), a clutch 74, and a brake 77.

The torsion spring 71 is coiled around the timing shaft 56 and has two hooked shaped ends. Shaft 56 is tubular. Adjacent the right end as shown in FIG. 6, the timing shaft 56 has a pin 79 (FIG. 6) which engages one of the hooked shaped ends of the spring 71. The gear 73 is rotatably mounted on the timing shaft 56 and the other end of the spring 71 is hooked in the web of the gear 73. In the hub 81 of the gear 73 are two radial slots 82 either of which can be aligned with an opening 83 in the wall of the shaft 56. The outer surface of the gear 73 engages with the brake 77 hereinafter described.

The clutch 74, in this instance, comprises an L-shaped rod 87 having a long portion and a short portion, and a pin 88 for pivotally mounting the rod 87 on the inside of the timing shaft 56. The rod 87 may be pivoted to move the end of the short portion through the opening 83 in the shaft 56 and into one of the slots 82 in the gear 73, thus locking the gear 73 to the shaft 56. When the clutch 74 is engaged, both ends of the spring 71 are secured to the shaft 56. The long portion of the member 87 extends out of the end of the shaft 56 so that the rod 87' can be manually moved to pivot the short portion out of the opening 83 and slot 82 to disengage the gear 73 from the shaft 56.

The brake 77, in this instance, comprises a rack 89 (FIGS. 3 and 7) secured to one end of a brake arm 91 and a spring 92 biasing the arm to move the rack into engagement with the teeth of the gear 73. The brake arm 91 is pivotally supported by a rod 93 which is secured to base unit 21, and the spring 92 is fastened to the other end of the brake arm 91 to bias the rack 89 toward the gear 73. A finger 94 is formed on the arm 91 so that the arm 91 may be manually moved to pivot the rack 89 out of engagement with the gear 73. Then with the brake 77 engaged, the adjacent end of the spring 71 is anchored to the base unit 21.

Considering the operation of the height-counterbalancing mechanism and the adjustment therefor, the counterbalancing force is provided by torsion spring 71 which tends to unwind and movethe board 23 and the column assembly 22 upwardly thus compensating for the weight of the board, the column assembly, and any objects mounted on the board 23. The amount of counterbalancing force may be adjusted by increasing or decreasing the amount of twist in the spring 71.

The force of the spring 71 may be adjusted by engagement and disengagement of both the brake 77 and the clutch 74. To engage the brake 77, the rack 89 is moved into engagement with the gear 73 by the spring 92. To disengage the brake 77, the draftsman presses the finger 94 downwardly to disengage the rack 89 from the gear 73. When the brake 77 is engaged, gear 73 cannot of course be rotated and thus one end of the spring 71 is fixed. To engage the clutch 74, the L-shaped member 87 is pivoted to move the short portion into the opening 83 and the slot 82. When the clutch 74 is engaged, both ends of the spring 71 are fixed to the shaft 56 so that the shaft may be turned without winding or unwinding the spring 71. During normal use of the table, the clutch 74 is disengaged and the brake 77 is engaged.

To increase the counterbalancing force, the brake 77 being engaged and the clutch 74 disengaged, the board 23 if in other than its lowermost position, is pushed downward causing the spring 71 to be wound more tightly and increasing the counterbalance force. With the board 23 in a lowermost position, the clutch 74 is engaged and the brake 77 then disengaged. If the force is not great enough, the board 23 is then raised and the above steps are repeated until the desired degree of counterbalancing force is achieved. After the desired counterbalancing force is achieved, the clutch 74 is disengaged and the brake is reengaged.

To decrease the counterbalancing force, the brake 77 being engaged and the clutch 74 disengaged, the board 23 if in other than its uppermost position is raised permitting the spring 71 to unwind and decreasing the counterbalance force. With the board 23 at its uppermost position, the clutch 74 is engaged and the brake 77 is disengaged. If the counterbalancing force is not decreased enough, the board 23 is lowered and the above steps are repeated until the desired degree of counterbalance is achieved. After the desired counterbalancing force is achieved, the brake 77 is left in engagement and the clutch 74 is left disengaged.

The drafting board 23 itself is of conventional construction, and to the underside of the board 23 there is secured a pair of laterally spaced channel-shaped supports 100. The tiltable mounting means 101 are connected to the supports 100. The tiltable mounting means 101 comprises two pairs of sets of brake leaves 102 and 103 (FIGS. 3 to 5), one set 102 being fastened to each support and one set 103 being fastened to the upper end of each column 36. The adjacent sets 102 and 103 are interleaved and pivotally connected together. One set of the brake leaves 102 is attached to each support 100 by means of pins 104 (FIG. 5) which extend through holes in the leaves 102 and the flanges of the channel supports 100.

To fasten the leaves 103 to the columns 36, each column 36 has an opening 107 in the front wall 108 thereof adjacent the upper end of the column. The opening 107 in each column has a top edge 109 and a bottom edge 111, and the rear wall 112 of the column has a hole 113 therein for a single fastening or bolt 115 (FIG. 4). The brake leaves 103 for each support column 36 are generally rectangularly shaped except for an inclined portion 114 on the lower edge thereof. The relatively narrow end of each brake leaf 103 has a hole 117. The pin 118 secures each set of brake leaves 103 to a U-shaped bracket 119 the arms of which embrace the set of leaves 103. The center portion 121 of each bracket 119 has a nut 122 secured thereto as by welding aligned with a hole in the center portion 121 of the bracket 119, the nut 122 receiving the bolt 115.

As shown in FIG. 4, the relatively narrow end portion of each leaf 103 has a width less than the height of the opening 107, whereas the relatively wide end portion has a width greater than the height of the opening. To assemble a set of the leaves 103 with a column, the narrow end portion of the leaves is inserted into the opening 107, and the bolt 115, which is in linear alignment with the set of leaves 103, is threaded into the nut 122. As the bolt 11S draws the U-shaped bracket 119 and the set of brake leaves 103 toward the rear wall 112 of the column, the edges 109 and 111 of the opening 107 engage the upper surface and the inclined portion 114 of the leaves 103 and wedge the brake leaves 103 in the opening 107. The adjacent ends of the leaves 102 and 103 are interleaved and pivoted on an inner tube 130 (FIG. 5).

The brake for the drafting board comprises the two sets of brake leaves 102 and 103, the inner tube 130, and an outer tube 131 which is concentric with the inner tube 130 but is shorter than the inner tube 130. The outer tube 31 is in two sections and a toggle 132 is intermediate the sections, and a lever 133 is attached to the toggle mechanism. Movement of the lever 133 causes the toggle 132 to move the two sections of the outer tube 131 apart and laterally outwardly, against collars 135 abutting the brake leaves 102 and 103. However, outward movement of the outermost of the sets of leaves 102 and 103 is prevented by collars 136 which on one end, the right end as shown in FIG. 5 abuts against a spacer 137 which in turn, abuts against one of the channels 100 secured to the board 23, and which on the other end abut against a mounting spacer 138 secured to the other channel 100. Further, inner tube 130 is secured on one end, the right end in FIG. 5, to one of the channels 100 as by welding, and the left end receives a nut 139 which clamps the flange of the other channel 100 between it and the spacer 138. The outward load imposed on the channels 100 by application of the brake is transferred from the channels to the inner tube 130. Consequently, the brake leaves 102 and 103 are pressed together to hold the board at a selected angle. The construction of the above brake, with the exception of the brake leaves, is generally similar to the brake disclosed in the previously mentioned Amthor et al. patent.

An adjustable counterbalance mechanism for the drafting board tiltable mounting is provided to facilitate tiltable movement of the board and comprises a torsion bar 140 having one end secured to the board 23 and the other end secured to one of the columns 36. The torsion bar 140 has a square-shaped cross section and has one end, the right end in this instance, a lever 141 which engages a pin 142 secured to the right-hand column 36. To the other end of the bar 140 is secured a set of discs I44. Interleaved between discs 144 is a set of discs 146, which are prevented from rotating by bolts 149. Bolts 149 pass through the plate 147, through the discs 146, through the holes in the leftmost channel 100, as shown in FIG. 5, and screw into the mounting spacer 138, and securely clamping the discs 144 and 146. The amount of counterbalance may be varied by increasing or decreasing the twist of the bar 140. Increased twist in bar 140 will result in increased counterbalance force.

To change the counterbalance force, the bolts 149 may be loosened permitting rotation of the discs 144 relative to the discs 146. The innermost disc 144 has a handle 150 which may be manually moved and rotates the discs 144 and the bar 140. After the handle 150 and bar have been rotated to increase or decrease the twist in bar 140 as desired, the screws 149 are again tightened.

It is apparent from the foregoing, that a novel and useful tiltable mounting for securing a drafting board to a drafting board column has been provided which comprises brake leaves for the board brake wedged in a column. It is also apparent that we have provided a novel adjustably counterbalanced drive mechanism for a drafting board column assembly which comprises a clutch and brake for securing the respective ends of the counterbalance spring to the drive mechanism and the drafting table.

We claim:

1. In a drafting table including base unit means, an adjustably counterbalanced column assembly, and a drafting board, said column assembly including at least one column, column drive means, and a counterbalance spring, one end of said spring being secured to one of said means, said adjustably counterbalanced column assembly comprising an intermediate element, the other end of said spring being secured to said intermediate element, the improvement comprising first means disengageably connecting said intermediate element to said column drive means so said intermediate element and said column drive means move together, and second means disengageably connecting said intermediate element to the other of said base unit means and said column drive means so said intermediate element is held against movement relative to the other of said base unit means and said column drive means, whereby said counterbalance spring for said column assembly is adjustable by selectively moving said column assembly while connecting and disconnecting said first and Second means.

2. A drafting table including a base unit, a column having at least two walls, and a drafting board, the improvement comprising means for tiltably mounting said drafting board on said column, said means comprising edges forming an opening in one of said walls, a plurality of brake leaves pivotally supporting said board, said brake leaves being the only support for said board, each of said leaves having a narrow portion narrower than said opening, a wide portion wider than said opening, and an inclined portion joining said other portions, and fastening means securing said brake leaves to said other wall of said column and wedging said inclined portion of said brake leaves between said edges of said column.

3. A drafting table as in claim 2 wherein said fastening means comprises a U-shaped bracket embracing and secured to the ends of said brake leaves, and means for adjustably securing said bracket to said column to draw said brake leaves into said opening and thereby wedge said inclined portion of said leaves between said edges.

4. In a drafting table including a base unit, an adjustably counterbalanced column assembly, and a drafting board, said column assembly including two columns, a column drive mechanism including a rotatable drive shaft, and a counterbalance spring, one end of said spring being secured to said drive shaft, an intermediate element rotatably mounted to said table, the other end of said spring being secured to said intermediate element, the improvement comprising a clutch releasably connecting said intermediate element to said column drive shaft so said intermediate element and said shaft rotate together, and a brake releaseably connecting said intermediate element to said base unit so said intermediate element will not rotate relative to said base unit, whereby said counterbalance spring for said column assembly is adjusted by selectively raising and lowering said column assembly while connecting and releasing said clutch and brake.

5. In a drafting table including a base unit, a drafting board, and an adjustably counterbalanced column assembly, wherein said drafting board is mounted for generally vertical movement on said column assembly, said column assembly comprising two vertically movable columns having racks secured thereto, a drive tube rotatably mounted on said base unit, gears rigidly secured to said tube and engaging said racks, a counterbalance spring encircling said tube and having one end secured thereto, another gear rotatably mounted on said tube and secured to the other end of said spring, the improvement comprising a brake rack pivotally mounted on said base unit and being movable to engage said other gear to prevent rotation of said other gear, and a clutch pin pivotally mounted on said drive tube and being movable to connect said tube to said other gear so said other gear rotates with said tube, whereby said counterbalance spring for said column assembly is adjusted by selectively engaging and disengaging said brake rack and clutch pin from said other gear while raising and lowering said column assembly.

6. A column assembly as in claim 5 wherein said clutch pin is L-shaped having long and short portions and is mounted in the interior of one end of said tube, said long portion extending axially out of said end of said tube for manual movement, and said short portion extending generally radially within said tube for engagement in radial holes in said tube and said other gear.

7. A drafting table comprising a base unit, a column assembly, a drafting board, and a plurality of brake leaves providing the sole tiltable mounting for said drafting board on said column assembly, said column assembly having at least two spaced walls and edges forming an opening in one of said waiis, said other wall being opposite said opening, said plurality of brake leaves arranged in sets, one set thereof being pivoted to the other, one of said sets being secured to said board, said brake leaves of the other of said sets having a narrow portion narrower than said opening, a wide portion wider than said opening, and an inclined portion joining said other portions, and fastening means engaging said other wall and said other set of leaves, said fastening means drawing said other set of brake leaves into said opening of said column assembly and \vedging said inclined portion of said brake leaves between said edges of said column assembly to secure said board to said column assembly.

8. A drafting table as in claim '7, wherein said fastening means comprises a U-shaped bracket, the ends of said bracket being secured to the ends of said other set of brake leaves, and the center of said bracket having a threaded fastener for adjustably securing said bracket to said other wall to draw said brake leaves into said opening and thereby wedge said brake leaves between said edges. 

1. In a drafting table including base unit means, an adjustably counterbalanced column assembly, and a drafting board, said column assembly including at least one column, column drive means, and a counterbalance spring, one end of said spring being secured to one of said means, said adjustably counterbalanced column assembly comprising an intermediate element, the other end of said spring being secured to said intermediate element, the improvement comprising first means disengageably connecting said intermediate element to said column drive means so said intermediate element and said column drive means move together, and second means disengageably connecting said intermediate element to the other of said base unit means and said column drive means so said intermediate element is held against movement relative to the other of said base unit means and said column drive means, whereby said counterbalance spring for said column assembly is adjustable by selectively moving said column assembly while connecting and disconnecting said first and second means.
 2. A drafting table including a base unit, a column having at least two walls, and a drafting board, the improvement comprising means for tiltably mounting said drafting board on said column, said means comprising edges forming an opening in one of said walls, a plurality of brake leaves pivotally supporting said board, said brake leaves being the only support for said board, each of said leaves having a narrow portion narrower than said opening, a wide portion wider than said opening, and an inclined portion joining said other portions, and fastening means securing said brake leaves to said other wall of said column and wedging said inclined portion of said brake leaves between said edges of said column.
 3. A drafting table as in claim 2 wherein said fastening means comprises a U-shaped bracket embracing and secured to the ends of said brake leaves, and means for adjustably securing said bracket to said column to draw said brake leaves into said opening and thereby wedge said inclined portion of said leaves between said edges.
 4. In a drafting table including a base unit, an adjustably counterbalanced column assembly, and a drafting board, said column assembly including two columns, a column drive mechanism including a rotatable drive shaft, and a counterbalance spring, one end of said spring being secured to said drive shaft, an intermediate element rotatably mounted to said table, the other end of said spring being secured to said intermediate element, the improvement comprising a clutch releasably connecting said intermediate element to said column drive shaft so said intermediate element and said shaft rotate together, and a brake releaseably connecting said intermediate element to said base unit so said intermediate element will not rotate relative to said base unit, whereby said counterbalance spring for said column assembly is adjusted by selectively raising and lowering said column assembly while connecting and releasing said clutch and brake.
 5. In a drafting table including a base unit, a drafting board, and an adjustably counterbalanced column assembly, wherein said drafting board is mounted for generally vertical movement on said column assembly, said column assembly comprising two vertically movable columns having racks secured thereto, a drive tube rotatably mounted on said base unit, gears rigidly secured to said tube and engaging said racks, a counterbalance spring encircling said tube and having one end secured thereto, another gear rotatably mounted on said tube and secured to the other end of said spring, the improvement comprising a brake rack pivotally mounted on said base unit and being movable to engage said other gear to prevent rotation of said other gear, and a clutch pin pivotally mounted on said drive tube and being movable to connect said tube to said other gear so said other gear rotates with said tube, whereby said counterbalance spring for said column assembly is adjusted by selectively engaging and disengaging said brake rack and clutch pin from said other gear while raising and lowering said column assembly.
 6. A column assembly as in claim 5 wherein said clutch pin is L-shaped having long and short portions and is mounted in the interior of one end of said tube, said long portion extending axially out of said end of said tube for manual movement, and said short portion extending generally radially within said tube for engagement in radial holes in said tube and said other gear.
 7. A drafting table comprising a base unit, a column assembly, a drafting board, and a plurality of brake leaves providing the sole tiltable mounting for said drafting board on said column assembly, said column assembly having at least two spaced walls and edges forming an opening in one of said walls, said other wall being opposite said opening, said plurality of brake leaves arranged in sets, one set thereof being pivoted to the other, one of said sets being secured to said board, said brake leaves of the other of said sets having a narrow portion narrower than said opening, a wide portion wider than said opening, and an inclined portion joining said other portions, and fastening means engaging said other wall and said other set of leaves, said fastening means drawing said other set of brake leaves into said opening of said column assembly and wedging said inclined portion of said brake leaves between said edges of said column assembly to secure said board to said column assembly.
 8. A drafting table as in claim 7, wherein said fastening means comprises a U-shaped bracket, the ends of said bracket being secured to the ends of said other set of brake leaves, and the center of said bracket having a threaded fastener for adjustably securing said bracket to said other wall to draw said brake leaves into said opening and thereby wedge said brake leaves between said edges. 